python中引用与复制用法实例分析
本文实例讲述了python中引用与复制用法。分享给大家供大家参考。具体分析如下：
在python中，任何不可变对象是传值的，而可变对象是传引用的。
不管是向函数传递参数或者是任何形式的对象复制来说，不可变对象（比如整数，字符串）被真正复制，而可变对象只是复制了一个对他们的引用，即在内存中只有一份对象，而引用两份。
a=b 这样的赋值，就会创建对b的引用，对于象数字和字符串这样的不可变的对象，这种赋值实际是创建了b的一个副本
>>> a='hello' >>> b=a >>> id(a) 29326432 >>> id(b) 29326432 >>> b is a True >>> a=1000 >>> b 'hello'
对于可变对象,比如字典和列表，a和b引用的是同一个对象，修改其中任意一个变量都会影响到另一个。
>>> a=[1,2,3,4] >>> b=a >>> id(a) 29280896 >>> id(b) 29280896 >>> b[3]='ccccccccc' >>> a [1, 2, 3, 'ccccccccc'] >>>
列表和字典这样的容器对象，可以使用两种赋值操作：浅复制和深复制。浅复制创建一个新对象，但它包含的是对原始对象中包含的项的引用。
比如下面的浅复制：
>>> a=[1,2,3,4,[9,0]] >>> b=a >>> a=[1,2,3,4,[9,0]] >>> b=list(a) >>> b is a False >>> b[0]=1000 >>> b [1000, 2, 3, 4, [9, 0]] #注意，b修改了b[0]以后，对a没有影响 >>> a [1, 2, 3, 4, [9, 0]] >>> b[4][1]='cccc' #注意，b修改了 b[4][1]以后，对a有影响 >>> b [1000, 2, 3, 4, [9, 'cccc']] >>> a [1, 2, 3, 4, [9, 'cccc']]
深复制将创建一个新对象，并且递归的复制它包含的所有对象，没有内置对象可以创建深复制，可以使用copy.deepcopy()函数完成。
>>> import copy >>> a=[1,2,3,[4,5]] >>> b=copy.deepcopy(a) >>> id(b) 29582240 >>> id(a) 29581840 >>> a is b False >>> b[0]=1000 >>> b [1000, 2, 3, [4, 5]] #注意修改了b[0]之后对a没有影响 >>> a [1, 2, 3, [4, 5]] >>> b[3][1]='gggg' >>> b [1000, 2, 3, [4, 'gggg']] #修改了 b[3][1]之后对a也没有影响，这是和浅复制的区别 >>> a [1, 2, 3, [4, 5]]
希望本文所述对大家的Python程序设计有所帮助。
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